An elastically stretchable composite sheet composed of an elastic sheet, which is formed of an elastically stretchable film or elastically stretchable continuous filaments, and a fiber aggregate having inelastic extensibility has been proposed in U.S. Pat. No. 6,730,390B1. The elastic sheet and the fiber aggregate are bonded to each other at discretely arranged bonds. The fibers making up the fiber aggregate are long fibers continuously extending between every adjacent bonds while describing irregular curves. The long fibers are independent of one another without being solvent welded nor thermally bonded between the bonds.
According to U.S. Pat. No. 6,730,390B1, because the long fibers of the fiber aggregate describe irregular curves between the bonds, the fiber aggregate does not interfere with the composite sheet stretch. However, since the long fibers of the fiber aggregate are independent of one another between the bonds, the elastically stretchable composite sheet has low strength against tension. The peel strength between the fiber aggregate and the elastic sheet is also low. Furthermore, the long fibers are liable to be raised between the bonds to cause a fuzzy appearance, which gives an unattractive impression.
Apart from the above described elastically stretchable composite sheet, various types of stretch nonwoven fabric containing elastic fibers made of elastomer resins are known. For example, U.S. Pat. No. 4,663,220A discloses an elastomeric nonwoven fabric including microfibers comprising an extrudable elastomeric composition containing at least about 10% by weight of an A-B-A block copolymer and a polyolefin. Containing a polyolefin, the microfibers cannot be designed to have sufficient stretch characteristics.
U.S. Pat. No. 5,385,775A proposes a composite elastic material which includes (1) an anisotropic elastic fibrous web having a layer of elastomeric meltblown fibers and a layer of elastomeric filaments and (2) a gatherable layer joined to the anisotropic elastic fibrous web. The material used to make the elastomeric filaments includes 40% to 80% by weight elastomeric polymer and 5% to 40% by weight resin tackifier. Containing a resin other than the elastomeric resin, the elastomeric filaments cannot be designed to have sufficient stretch characteristics.
JP 2002-361766A discloses a stretchable composite sheet including an elastic sheet formed of fiber or film containing 60% to 99% by weight of a styrene elastomer having a styrene content of 10% to 40% by weight and a number average molecular weight of 70,000 to 150,000. The fiber or film contains a material other than the styrene elastomer, such as an olefinic resin or an oil component. On account of the material other than the elastomeric material, the stretchable composite sheet cannot be designed to have sufficient stretch characteristics.
JP 4-11059A discloses a stretch nonwoven fabric formed of fibers of a styrene elastomer. The styrene elastomer is obtained by preparing a block copolymer composed of a styrene-based polymer block A and an isoprene-based polymer block B and hydrogenating the isoprene double bonds. The nonwoven fabric has a low modulus and cannot be regarded as having sufficient hysteresis of extension and retraction.